Centrifugal chillers utilizing low pressure refrigerants operate at less than atmospheric pressure. When the unit is running, air and moisture may leak into the machine through low pressure areas, and may accumulate in the condenser during machine operation. The air in the condenser increases condensing pressure, increases compressor power requirements, and reduces the chiller's efficiency and cooling capacity.
A purge system is provided on all low pressure refrigerant centrifugal units to remove moisture and other non-condensibles that may leak into the machine. Known purge systems typically include a condenser to recapture refrigerant before it is exhausted into the atmosphere. The effectiveness of standard purge systems is limited, however, and even when operating properly purge units discharge substantial amounts of refrigerant into the atmosphere. Losses can be as much as eight pounds of refrigerant for every pound of air purged from the chiller.
The loss of refrigerant during the purge cycle is particularly disturbing in view of the fact that low pressure refrigerants typically include chlorofluorocarbons (CFC's) which are known to be especially hazardous. Further, due to the increased environmental risk posed by low pressure refrigerants, the cost of those refrigerants has increased significantly in the past several years.
The cost of replacing the entire purge system of an existing low pressure centrifugal chiller can be tens of thousands of dollars. In many cases, the cost of replacing the entire purge system of an existing low pressure centrifugal chiller is not justified considering the economics of the firm in which the chiller is used. However, an auxiliary purge system which can be retrofitted to the existing purge system may be economically feasible if it utilizes the components of an existing purge system to provide the first level of refrigerant recovery and dehydration. The auxiliary purge unit can then complete the refrigerant recovery process, providing a significant reduction in the release of environmentally hazardous compounds at an acceptably low cost.
A need therefore exists for an auxiliary purge unit which provides superior refrigerant recovery efficiency, and which can be retrofitted to the existing purge unit of a low pressure chiller to significantly reduce hazardous emissions at minimal cost. The present invention addresses that need.